This project aims to identify possible environmental endocrine disrupters working by an unusual mechanism that operates after the interaction of ligands with nuclear hormone receptors, namely, by the direct inhibition or potentiation of the nuclear hormone receptor/coactivator interaction itself. This goal will be accomplished by developing time-resolved fluorescence assays that probe in a robust and reliable manner the interaction of the nuclear receptors with coactivators. These assays are adaptable to high-throughput screening, and will be used at the Emory University Molecular Libraries Screening Center, an NIH-funded Roadmap Research Resource to which we have obtained access, to identify possible coactivator binding inhibitors (CBIs) or coactivator binding potentiators (CBPs) that might be present in the environment. After compounds have been identified as possible disrupters or potentiators of endocrine function, they will be subject to secondary assays to confirm that they indeed act through these unusual CBI or CBP mechanisms. These assays will also use fluorescence resonance energy transfer methodology, but with carefully selected alterations in the concentrations of integral components to elucidate mechanism. Finally, cell-based assays such as mammalian-2-hybrid, cotransfection reporter gene assays, or monitoring of hormone-responsive gene products will more definitively demonstrate the possible biological or physiological effects arising from exposure to these compounds. This project should help pinpoint a novel endocrine disruption site within the nuclear receptor signaling pathway and identify the compounds that work at this level. It should also help identify possible CBIs or CBPs present in the environment or in commonly used products that could be causing alterations in the pattern of genome transcription by an unusual mechanism, due to the interruption or the potentiation of nuclear receptor-regulated signal transduction that operates at a post ligand-receptor interaction level. Ultimately, this project should help in identifying harmful compounds present within our environment and, hopefully, guide measures to minimize exposure of the public to these substances. Endocrine disrupters are exogenous compounds that interfere with the endocrine system, altering hormone action and the messages it sends throughout the body. This project aims to identify possible endocrine disrupters that act by an unusual mechanism. Large numbers of compounds will be screened to determine structural featurs of those that inhibit or potentiate endocrine action by this unusual process. With this information, steps could be taken to minimize human exposure to these novel types of endocrine disrupters.